Cool concept! I really like the idea of getting to build a world while you also build your little city. Combining items is a nice and simple way to manage resources. It would be really awesome to see how this could develop (i.e. maybe you could be forced to put down negative tiles which develop on their own, leading the player to build strategically to support/fight/etc).
Anyway, obviously this concept is quite ambitious for a jam, and it looks like you had a lot of other plans too... but you did good to get this much done.